Preparation of organic acid esters of cellulose



Patented July 15, 1952 for CELLULQSEV 3 --Peter Blackman, W'estfield, and'Fred Fortess and Blanche B. White; Summit, N.'J., assignors to Celanese Corporation ofrmnerica, ;New N. LY a corporation of Delaware;

No Drawing. AppHcation'May 18,1950,

York,

""Serial'No. 162,826

r This invention relates tothe preparation-of organic acid esters of celluloseand relates more particularly to an improved process for the treatment of cellulosic material that is to' be employed for the production of organic aeidesters'oi cellulose ' -In the production of organic acid estersof cellulose'from cellulosic material, it is'the general'practice to pretreat thecellulosic material 'prior to esterification to increase its reactlvityi The pretreated cellulosic material'is thenesterifled with an organic acid anhydride, usually "in the 5 presence of an esterification catalyst; such as sulfuric acid, and an organicacid, such as acetic acid, which acts asa solvent 'for-the cellulose ester beingiornied. The; pretreatment oi; the cellulosic material greatly reducesfthe time required for the esterification. However, the-pre treatment does not always impart the same re activity to difi erentbatches of cellulosic material frorn'ja-given source so that the time required tor their-"esterification will vary appreciably. While provision can be made in a-batch esterifica ion process to adjust the esterification time accordance with changes in the reactivityflof the j cellulosic material, there is an additional expensefinvolvedin making this adjustment; In a; continuous process, on the other hand, the esterification time cannot be adjusted readily in accordance with changes in thereactivity of the cellulosic material. It is, accordingly, necessary, 'ir'rfa" contj muous process, to provide a sufiicient esterificationtinie tocomplete the esterification of f the least reactive cellulosic material. As'will bereadily apparent, this increase in the time provided.for esterification will reduce thecapacity of the esterificatio-n equipment and increase the esterification cost. v a 1?,Notjonlydoes the pretreatment fail to impart the same reactivity to different batchesvoi cellulosic material from a given source, but it also fails to impart the same reactivity to all the eellulosicmaterial in a single batch. That portion of the cellulosic material in a single batch which hasa lower reactivity is esterified more slowly cellulosic material from a given'source will have substantially mentfhlwnv H '{Another object of this inventionis to provide a process for treating cellulosic material that is t'o be employed for the production of organic the same reactivity afterfpretreate acid esters of cellulose so that all the cellulosic thanthe remainder of the cellulosic materialfin said jb'atch; .To insure the esterification of the least'reactive cellulosic material in a batch, the esterigfication time must be lengthened considerably, further reducing the capacity of the esterification equipment and increasing the esterification cost.-

[It is an. important object of thisinvention to provide a process for thepreparation oilorganic acid esters ofcellulose which will be free vfrom material in a single batch will'have substantially the/same reactivity after pretreatment.

A still further-object of this invention is to provide a process for treating cellulosicmaterial that is to'be employed for the production of or gani'c acid-esters of 'cel1ulose so' that the cellulosic material will have ahigher reactivity after pretreatment in Y, r Other'objects" of this-invention win be'apparent' from the following detailed description and claims'lf f" I t "It" has been foundthat'the variations'g a'fter pretreatment, in the reactivity "of difiere'nt batches of cellulosic material from a given-source and indifferentportions of a single-hatchet cellulosic materialare theresult of differences both'in moisture content of the cellulosic material immediately prior to-pretr'eatment and in the moisture history" ofsaid cellulosic material.

Thus, as thernoisture content of" the cellulosic material fallsbelow-about 5% by weight, there is a corresponding decrease inthe reactivity'of said cellulosic material after pretreatment. 'When the moisture content of the" cellulosic material fall's further to below about 4% by weight thereis an accelerated decrease in the reactivity ofthe celilulcsic material after pretreatment so that when the-moisture contentjoi the cellulosic: material fallsto below about 3% by Weight, the'pretreatmer t has substantially rioeffecton the reactivity of the cellulosicmaterial; The phrase cellulosic ma'terial' from" a given source employed herein denotes cellulosic material derived from asingle type of plant such as cotton-lint'ers, wood pulp,- .etc.:that has been purified by the sameprocess. l .7 .7 Another factor that determines the reactivity .of the cellulosic material after pretreatmenteis the .moisture history of thegcellulosic, material. For examplaif a batchof cellulosic-material having a given moisture content is pretreated,

its reactivity after pretreatment will dependupon 1 whether the moisture content of said cellulosic material has previously been below about 5% by weight. A cellulosic material whose moisture a cellulosicmaterial whose moisture content had dropped below said value and then been raised to said value before pretreatment. This differ b ence in'the reactivity of the cellulosic material sired value, at least about'5% or preferably at least about by weight of water is evaporated from the cellulosic material without, however,

' permitting the moisture content of the cellulosic materialto fall below about 4.5 or preferably below about 5.'%;jby weightl- Preferably: a sumcient quantity of'water is evaporated from the cellulosic material to reduce its moisture content to between about Band 7% by weight, since,

after pretreatment is particularly marked .when'fmigi'f 'a la-rg'er quantity-of water is permittedto rethe moisture content or the cellulosic material' falls'to less than" about 1%: by weightgbefore pretreatment and is subsequently?raisedito higher value. Since both the moisture content and the moisturehistory of different batches of cellulosic material from a given-lsource-or in different portions of a single batch'of'cellulosic material may vary as the result of variations conditions during the production and 'storagef o'f said cellulosic material,,xthere is a considerable 0 variationin the reactivity of the cellulosic ma:- terial.after pretreatment. According; to the presentinventiomgwe have 1 discovered, that theyariations;-.after pretreatment,;:in: the reactivity ofdifferentzbatchesf of cellulofsic materia'rfrom agiven source and in-different portions: of a singlebatch ofeellulosie materialrmay-be" eliminated bybringing the moisture content of said cellulosic material to at least about 115% -by .weight,; and evaporating; at least, -about 151% 101* preferably at" least aboutlo by: weight orz-wateron the weight ofthe cellulosic material from: the I cellulosic materiah without, however, reducing: the -moisture content--ofthe cellulosic materialto less than about4.5% or preferably 5 less' than' about 5%- by weight.=- Upon pretreatment of: cellulosie material that=has been treated I in =-this ma-nner,;there is obtained-a product hav ing=a uniiormyreacl ivity both? as-between d-ifier-jente liulo i -rmater al f oma en 40 source and as between different portions: -o1 E-;;a single;batch of cellulosie;--material.1 The process of. ..--,this7 invention is especially advantageous in treating cellulosic material whose moisture-eon,- tenthad-dropped below about- 1% by weight since this cel'lulosic materialfls extremelyresistant to Y, 4 M losic material to at least about 90% weight, for,

activation =du ring-the pretreatment: process.

In: carryingout the treatment of this invention a-sufficientrquantity of moisture is added-to the;cellulosicymaterial tobring. the-moisture con 'tent of said materialteat least about,-; 15%; by

weight ng advantageously,. to betweenabout. 15

' and-3Q??? by weight, Theadditionof a-greater quantity ofv water to-the cellulosic. materialwill not makeathe reactivity of the cellulosic materialgatter pretreatment, less uniform However,

the-addition; ofthis greaternuantity ofwater isrelativelyundesirable,when the water is added simply to makemore uniform the: reactivity .of

. the-cellulosic material aftr. pretreatment, since n15 additional water :m-ust :eit l'ier 'beevaporated from the .cellulosicamaterial or} permitted: to remain f izi thelcellulo'sie material, it. will react with. the. organic acid :anhydrideemployed in the. esterifioation medium, converting the" same material eiSfIEL'iSBd to at least about.l5'% by weight.

To this end, the water may 'be sprayed onto a mass of cellulosic fibers and the mixture-stirred thoroughlyuntil the desired' distribution has' efi ectede After the 'moisture content' of thetele 7 main in the cellulosic material, the additional waterwill react with the organic acidanhydride employedflforthe' esterification, converting the same toflthe corresponding organic acid. The evaporation of the water from the cellulosic material may beefiected rapidly by blowing an evaporaj,itive,rhedium such as air through said material. The evaporative medium may be heated to a. temperature of between about 25 and 65 C., or more, if desired, to increase the 7 rate of evaporation. (lare should be taken, :in this case, to avoid overdryin -Ea ly po t n of. t e; 1 10 mat r -i since overdrying will both .reduce, ;an-dmake: non' u iform the; re ti t a te pr r at e t;o the cellulosiamaterial; I The addition of-water to the cellulosic material and the subsequent evaporation-of the: water therefrom can be carriedoutvery rapidly. Thus,

the addition; of water .to the cellulosic material G JFL- IW LCfiected, with; agitationinas littlep as about; 19 1 seconds or in from about; 10- to/ 60 sec;- o l az-whi it e r m md the w ierF m efiected: in as little t re h si material-w seconds. Although longer periods oi time may be employedbothfor adding thewater toL the cellulosic material and forevaporatingthewater invention can .be carried out-makesit applicable esses.--

to bbthfbatch and cont n o s esterificationprbc- [B' when the mer ing! :content offthe dam;

advantageously, to between; about 90 and by weight, before evaporating the ater there} from, it is tpossibl'eglin i cert'ai'ri'lca' s, not. onlyflto make more uniform," but"; also? to fincreasej l con;-

, i, Q ofitlie' eenulesiematenariaaer pretreatment. Infthis 'ca'se,',..at ,least about 80%. by ,weight' 6 water is evaporatedfrom thev cellulo'sic material beforelth'e pretreatment; without, however, permitting jche' moisture icontent to i ran; below .abolit 4.5%?"01;"prereramyibe; low about 5%"by weight. I a "I Following the evaporation ofl the water the oellulosic; materialf'is pretreated; to? increase its reactivit'y i'n' av manner 'welfknownfin, the art; For example the ,cellulosicQmaterialrnaykbe treat ed; with; a lower aliphatic facidl'such'fa's formic,

siderably the. reactiv acetic orfpropionic acid, .or mixtures" thereof; "or

13.. SlTapplication'jNo; 58,028, filed November? 2',

1948; The pretreated cel'lulosic material is then es'terifid with an organic acid anhydride 'in'a I manner well known in the art preferably'inithe inane material has beenadjusted to" "mafi '1 presenceiof"anesterification catalyst"- and an or ganic'acid hic'h' acts as" a solvent for the'celiuloseester being formed;

complete the esterification 1 The cellulosic-material that has been treated in accordance with'this invention exhibits a sub-- stantially' uniform reactivity, afterpretreatment, bothas between different batches of cellulosic material from 'a givensource and. as between different portionslof a single batch of cellulosic material as evidenced. by the reproducibility of the time .required to complete the esterifi'cation. Moreover, whenthe moisture content of the cellulosic material has been raised to above about 90% by weight, it exhibits, in certain cases, not onlya more uniform reactivity after pretreatment,:but also a greatly increased reactivity after pretreatment, thereby permitting the esterifi-cation time withia given esterification process to be "reducedup to about 30% or evenmore.

The moisture content of the cellulosic material as set forthherein is measured on the dry weight .oiE. the cellulosic material, 1. e; a'cellulosic material having-a moisture content of by. weight .contains5partsby weight of water for every'l00 .parts by weight of the dry cellulosic:material.

- The-process of the: present invention may be applied. to any suitable cellulosic materiaLLsuch as cotton linters,.or wood pulp's or, the like from which the major portion of the lignin, pentosans, resins and similar constituents .have been removed;.as, for example, purifiedsulfite pulp, sul- Iatefipulp or soda pulp. In addition, there may befiemployed cellulosic material derived'xfrom othersources such as bamboo,.reeds, jute, esparto, straws,; such as linseed and hemps-eed straw, grasses, peanut hulls, bark, etc. The cellulosic material is advantageously pretreated in the form of' a mass of loose fibers to permit ready access of the added water to all portions of the fibers and to permit the water to'be evaporated uniformly irom'the fibers.

While our invention will be especially described in connection with the preparation of cellulose acetate, it is to be understood that it is also applicableto the preparation of, other organic acid esters of cellulose such as thesimple and mixed lower aliphatic acid esters of cellulose including cellulosev propionate', cellulose butyrate, cellulose acetate-propionate. cellulose acetate-butyrate and the like. In addition, it is applicable to the preparation of other organic acid esters of cellulose such as cellulose acetate stearate, as well as to the benzoic acid ester of cellulose.

Thefollowing examples are given to illustrate the invention further: I

Example I (Cotton linters having a moisture content of 5.74% by weight are oven dried for 2 hours at 100919., reducing their moisture content to 0.24% by weight. Portions of both the ovendried and the undried cotton linters are separately pretreatedby adding to 60, parts by weight of the cottonlinters, 21 parts; by weight of glacial acetic acid-,containing 0.3 parts by weight of sulfuric acid and agitating the mixture so formed for 2 "hours. The pretreated cotton linters are cooled :to 3pto 8 C. and. esterified by treatment with a cooled to. 3 to'5 C. and containing 399 parts by, weightof glacial acetic acid, 177 parts by 'weight' of acetic anhydride and 7.6 parts by weight of sulfuric acid. The time required to of the undried cotton -linters, as evidenced by the clearing of the esterification medium, is 25 minutes whereas the dried cotton linters are not fully esterified after 45 minutes,- an increase in esteriiication time of more than 80%. 7

dried, showing that the cotton linters have not regained theiroriginal' reactivity although their moisture content has been restored to substantially its original value.

I EmampleI II Y A sample-o f the dried cotton linters produce in-Example I is mixed for 10 seconds with-15.9%

by weight of waterand is then dried to a moisture' content of 5.61% by Weight byblowing air heated to a temperature of 62"C.-through*the cotton linters for 50 seconds. The cotton linters are then pretreated and esterified in'the manner set forth in Example I. The time required-to complete the esterification of the cotton linters treated iIl'thiS manner is substantially the same as that required to esterify the cotton linters thathave not been dried, showing that the cotton linters haveregained their original reactivity although their moisture content is somewhat lower than its original'value.

Example IV cotton linters are then pretreated and esterified.

in the manner set forth in Example I. The time required to complete the esterification of the cotton linters treated inthis manner is27=% less than that required to esterify-the untreated cotton linters, showing that the cotton linters have an increased reactivity. 71

It is to be understood that the foregoing detailed description is given merely by way of illustration arid that many variations may be made therein without departing from thespirit of-our invention.

Havingdescribed our invention, what we desireto secure by Letters Patent is:

1" ,In a process for the'produc tion of lower aliphatic acid esters of cellulose by the esterification of acellulosic material, the steps of increasing the activity of cellulosic material by adding moisture to cellulosic material in the form of a mass of loosefibers, which cellulosic material without said additional moisture wouldnothave its reactivity increased, to bring the moisture content of the cellulosic materialto at least about 15% by weight, evaporating from the cellulosic material at least about 5% by weight of moisture on the'weight of'the cellulosic material without reducing the moisture content of the cellulosic material to less than about' 4.5%

.lu losic: material without tobetw'een about 90 and 100% crating from the cellulosic .materialsuflicient moisture" to j'bringthe "moisture content .of the cellulosic material 'to between about and 7% by. weight, pretreating the cellulosic material by 1 adding a lowena'l'iphatic' acid .theretowithout' creasing the activityfof cellulosic material by adding moisture to cellulosic material. in the form offa mass or'jmose fibers, which cellulosic material without said additional moisture would notfhave'its. reactivityfincreased, to bringf'the 'moisture content, of the cellulosic material to aliphatic acid esters fof cellulose bythe esterification of a. cellulosic material, the steps ofrincreasing the-activity of cellulosic materialby addingmoistureto cellulosicv material in-the form of a mass of loose. fibers, which cellulosic material without said additional moisture would not haveits reactivity increased, to bring the moisture content of the cellulosic material to between about and %v by weight, evaporat.

from the cellulosicmaterial sufficientmoisture. to bring the moisture content of the cellulosic material to between about 5 and 7% by weight, pretreating the cellulosic material; by

adding a lower aliphatic. acid thereto Without displacing the moisture contained therein, and esterifying the pretreated cellulosic material with; a lower aliphatic acid anhydride.

-4, In .a process for theproduction of lower aliphatic acid esters of cellulose by the esterification of a cellulosic-material .thesteps which comprise adding moisture to cellulosic. material inwtheform of a mass of loose fibers to .bring the moisture content of the cellulosic-material toat least about 90% lay-weight of moi sture on the weight of the celreducing the moisture con tentgof the cellulosic material to less .;than about 4.5% by weight, pretreatingthe cellulosic Y material by adding a. lower aliphatic acid thereto without. displacing the moisture contained therein, and esterifying the pretreated cellulosic material with a lower aliphatic acid anhydride.

5; In a process for the production of lower aliphatic. acid esters of celluloseby-the'esterification of acellulosic material,..the steps which comprise adding moistureto cellulosic material in'the form of a mass of loose fibers to. bring by weight of moisturecn the-weight .of thecel 'lulosi'cmaterial withoutmeducingi the moisture content of the. cellulosic material; to less than about; 4.5% by .weight, "pretreating the, cellulosic material by adding a. lower aliphatic-acidstherev by weight, evaporating, fromxthe cellulosic material at'least about 80% V the moisture content of the cellulosic material displacing the i moisture contained therein, and

I by weight, evap- Iestei'ifying the pretreated cellulosic material with a lower aliphatic acid .anhydride;

6. 'In aprocess for the production of lower aliphaticacid esters ofcellulose by the esteri adding; moisture to cellulosic material'in. the

[form of a mass of loose fi-bers, which cellulosic material withoutsaid additional moisture would at; least about 15% by Weight, passing airyhavfication of a cellulosic material,. the steps of. increasing the activity ofcellulosic material by 'anhydride. 1 g

' 9. In a process for the :prod'uctionof cellulose about 5% t v of. the cellulosic. material without. reducing the tolwithout: displacing.;the moisture contained therein,-- and esterifying. .the pretreated. cellulosic material with alower aliphatic acid-.anhydride.

7..In .a-procss. for theproduction:of lower aliphatic acid. esters. of). cellulose by the. esteriificationof a cellulosicrnaterial, the StEDS.:.Qf-'1Tir.

creasing the activity of cellulosic material by adding moisture to. cellulosic..materialr-in the 'form of a mass; of loosefibers,whichcellulosic material. without said additional moisture would not..have .its reactivity increased, a, period of:,f-rom HbOtltflO to; 6.0.seconds. to, bring the moisture content :of the cellulosic. material-to at. least about: 15% by weight, evaporating from the cellulosic material gate least about .5%. by weight of moisture. on the. Weightsof. thelcellulosic material in'a period: 'of-ffrom about .50

to ISO-seconds; without. reducing the moisture content ofthe cellulosic. material. to. lessaithan about 4.5 by weight, pretreating-the cellulosic material by adding. a lower aliphatic acid there.- to 'without displacing the "moisture contained therein; and esterifying the pretreated cellulosic material with a lower aliphatic acid anhydride.

1 8." In a process for the production ,oflower aliphatic acid esters ofcellulose by the. esterificati'on 'of'a cellulosic materiahthe steps which comprise adding moisture to. cellulosic. material in the form. of a mass of loose-fibers: and hav ing a moisture content of less. than 1% by weight to bring the moisture content of J the cellulosic material to at least about '15%'by weightevapcrating from the cellulosic .material at least about5% by weight of'. moisture .on the weig-ht of the cellulosicmaterial. without reducing th'e moisture content of the cellulosic material to less than about-4.5% by weight,pretreating'the cellulosic material by adding a loweraliphatic acid thereto without displacing the moisture contained therein, and esterif'ying the pretreated cellulosic material with a lower aliphatic ac'id acetate by the acetylation of a cellulosic material, the steps of increasingthe activity of cellulosic material byad'din'g moisture to cellulosic material in the form of. a mass of loose fibers,

which cellul'osicmaterial without said additional.

moisture .{Would not, have. its reactivity increased, tojbring. the moisture content of the, cellulosic material to at least about-15% by Weight, evaporatingI-frfom thel cellulosic material. atQle'a'st by. weight .of moisture on the weight.

moisture content. of thej cellulosicimaterial; to

lessjthan about 4.5% .by weight, .pretreating the. cellulosic. material. by adding a lower aliphatic acidl thereto iwithout. displacing the moisinirev contained. therein, and. acetylating the pro-- treated cellulosic'material withlacetic anhydride. 1-0.' In1,a process for the production of cellulose acetate by the acetylation...of a cellulosic material, the steps of increasing the activityof cellulosic material by adding moisture to, cellulosic material: in the form of a .mass of loose fibers; which cellulosic materialwithout saidadditional moisture would not have its reactiyity increased, to bring the moisture content of the cellulosic material to at least about 15% by weight, evaporating from the cellulosic material'at least about 10% by weight of moisture on the weight of the cellulosic material without reducing the moisture content of the'cellulosic material to less than about by weight, pretreating the cellulosic material by adding a lower aliphatic acid thereto without displacing the moisture contained therein, and acetylating the pretreated cellulosic material with acetic anhydride.

11. In a process for the production of cellulose acetate by the acetylation of a cellulosic material, the steps of increasing the activity of cellulosic material by adding moisture to cellulosic material in the form of a mass of loose fibers, which cellulosic material without said additional moisture would not have its reactivity increased, to bring the moisture content of the cellulosic material to between about 15 and 30% by weight, evaporating from the cellulosic material sufiicient moisture to bring the moisture content of the cellulosic material to between about 5 and 7% by weight, pretreating the cellulosic material by adding a lower aliphatic acid thereto without displacing the moisture contained therein and an esterification catalyst, and acetylating the pretreated cellulosic material with acetic anhydride.

12. In a process for the production of cellulose acetate by the acetylation of a cellulosic material, the steps which comprise adding moisture to cellulosic material in the form of a mass of loose fibers to bring the moisture content of the cellulosic material to at least about 90% by weight, evaporating from the cellulosic material at least about 80% by weight of moisture on the weight of the cellulosic material without reducing the moisture content of the cellulosic material to less than about 4.5% by weight, pretreating the cellulosic material by adding a lower aliphatic acid thereto without displacing the moisture contained therein, and' acetylating the pretreated cellulosic material with acetic anhydride.

13. In a process for the production of cellulose acetate by the acetylation of a cellulosic phatic acid thereto without displacing the moisture contained therein and an esteriflcation catalyst, and acetylating the pretreated cellulosic material with acetic anhydride.

PETER BLACKMAN. FRED FORTESS. BLANCHE B. WHITEI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,543,310 Altwegg June 23, 1925 2,063,324 Malm et a1. Dec. 8, 1936 2,087,263 Olsen July 20, 1937 2,105,498 Parrett et a1. Jan. 18, 1938 2,113,301 Gardner Apr. 5, 1938 2,119,117 Schuller May 31, 1938 2,345,406 Malm Mar. 28, 1944 2,478,396 I-Iincke et a1. Aug. 9, 1949 2,484,455 Herdle et a1. Oct. 11, 1949 2,487,892 Richter et a1. Nov. 15, 1949 2,490,754 Hincke et al. Dec. 6, 1949 FOREIGN PATENTS Number Country Date Great Britain 1938 OTHER REFERENCES Worden, Technology of Cellulose Esters, vol. 8, 1916, page 2567. 

1. IN A PROCESS FOR THE PRODUCTION OF LOWER ALIPHATIC ACID ESTERS OF CELLULOSE BY THE ESTERIFICATION OF A CELLULOSIC MATERIAL, THE STEPS OF INCREASING THE ACTIVITY OF CELLULOSIC MATERIAL BY ADDING MOISTURE TO CELLULOSIC MATERIAL IN THE FORM OF A MASS OF LOOSE FIBERS, WHICH CELLULOSIC MATERIAL WITHOUT SAID ADDITIONAL MOISTURE WOULD NOT HAVE ITS REACTIVITY INCREASED, SO BRING THE MOISTURE CONTENT OF THE CELLULOSIC MATERIAL TO AT LEAST ABOUT 15% BY WEIGHT, EVAPORATING FROM THE CELLULOSIC MATERIAL AT LEAST ABOUT 5% BY WEIGHT OF MOISTURE ON THE WEIGHT OF THE CELLULOSIC MATERIAL WITHOUT REDUCING THE MOISTURE CONTENT OF THE CELLULOSIC MATERIAL TO LESS THAN ABOUT 4.5% BY WEIGHT, PRETREATING THE CELLULOSIC MATERIAL BY ADDING A LOWER ALIPHATIC ACID THERETO WITHOUT DISPLACING THE MOISTURE CONTAINED THEREIN, AND ESTERIFYING THE PRETREATED CELLULOSIC MATERIAL WITH A LOWER ALIPHATIC ACID ANHYDRIDE. 